1. Field of the Invention
This invention relates generally to downhole tools, and more particularly to a jar that is operable to impart axial force to a downhole string and that is equipped with a conductor for carrying electrical current.
2. Description of the Related Art
In oil and gas well operations, it is frequently necessary to inflict large axial blows to a tool or tool string that is positioned downhole. Examples of such circumstances are legion. One situation frequently encountered is the sticking of drilling or production equipment in a well bore to such a degree that it cannot be readily dislodged. Another circumstance involves the retrieval of a tool or string downhole that has been separated from its pipe or tubing string. The separation between the pipe or tubing and the stranded tool or xe2x80x9cfishxe2x80x9d may be the result of structural failure or a deliberate disconnection initiated from the surface.
Jars have been used in petroleum well operations for several decades to enable operators to deliver such axial blows to stuck or stranded tools and strings. There are a few basic types. So called xe2x80x9cdrilling jarsxe2x80x9d are frequently employed when either drilling or production equipment has become stuck to such a degree that it cannot be readily dislodged from the well bore. The drilling jar is normally placed in the pipe string in the region of the stuck object and allows an operator at the surface to deliver a series of impact blows to the drill string via a manipulation of the drill string. These impact blows to the drill string are intended to dislodge the stuck object and permit continued operation. So called xe2x80x9cfishing jarsxe2x80x9d are inserted into the well bore to retrieve a stranded tool or fish. Fishing jars are provided with a mechanism that is designed to firmly grasp the fish so that the fishing jar and the fish may be lifted together from the well. Many fishing jars are also provided with the capability to deliver axial blows to the fish to facilitate retrieval.
Jars capable of inflicting axial blows contain a sliding joint which allows a relative axial movement between an inner mandrel and an outer housing without necessarily allowing relative rotational movement therebetween. The mandrel typically has a hammer formed thereon, while the housing includes an anvil positioned adjacent to the mandrel hammer. Thus, by sliding the hammer and anvil together at high velocity, a substantial jarring force may be imparted to the stuck object, which is often sufficient to jar the object free.
Some conventional jars employ a collet as a triggering mechanism. The collet is provided with one or more radially projecting flanges or teeth which engage a mating set of projections or channels in the mandrel. The engagement of the collet teeth and the mandrel teeth or channels restrains the longitudinal movement of the mandrel until some desired trigger point is reached. The trigger point frequently corresponds to the vertical alignment between the collet teeth and a channel or set of channels in the tool housing. At this point, the collet is no longer compressed radially inwardly and can expand rapidly in diameter to release the mandrel. The surfaces of the collet teeth and the channel or channels of the housing engaged just prior to triggering may be subject to significant point loading, which can lead to rapid wear and the need for frequent repair. Furthermore, some conventional designs do not provide structure to prevent the premature expansion of the collet, which can otherwise lead to a sticking of the mandrel or a premature triggering. Premature triggering can lead to diminished overpull and application of less than desired axial force.
Many well operations are presently carried out with strings that utilize electrical power. Such tool strings are often suspended from conducting and non-conducting cables, such as wirelines and slicklines. In some wireline and slickline operations, it may be desirable to deploy a jar with tool string. If the jar is incapable of transmitting electrical power and signals, it must be positioned in the bottom hole assembly (xe2x80x9cBHAxe2x80x9d) below the electrically powered components of the BHA. However, this may not be the optimum position for the jar in view of the operation to be performed.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a downhole tool is provided that includes a housing and a mandrel telescopically positioned in the housing with an electrically insulating coating. The mandrel and the housing define a pressure compensated substantially sealed chamber containing a volume of a non-conducting fluid. A conductor member is insulatingly coupled to the housing. A portion of the conductor member is electrically insulated from an ambient fluid by the non-conducting fluid. A first biasing member is provided for maintaining a conducting pathway between the mandrel and the conductor member, engaging the mandrel, and a sleeve positioned around and being axially moveable relative to the collet, the sleeve having a reduced inner diameter portion at which the collet selectively expands radially to disengage the mandrel.
In accordance with another aspect one aspect of the present invention, a downhole tool is provided that includes a housing with an external vent and a mandrel telescopically positioned in the housing. The mandrel has an electrically insulating coating. The mandrel and the housing define a chamber in fluid communication with the vent. The mandrel has a first pressure area in fluid communication with the chamber and a second pressure area of substantially equal area to the first pressure area whereby ambient fluid pressure acting on the first and second pressure areas hydrostatically balances the mandrel. A conductor member is insulatingly coupled to the housing and is electrically insulated from the ambient fluid. A first biasing member is provided for maintaining a conducting pathway between the mandrel and the conductor member.
In accordance with another aspect of the present invention, a downhole tool is provided that includes a housing and a mandrel telescopically positioned in the housing. The mandrel and the housing define a pressure compensated substantially sealed chamber containing a volume of a non-conducting fluid. A conductor member is positioned in the housing for providing an electrically conducting pathway. The conductor member has a first segment and a second segment. The first segment is moveable with the mandrel and relative to the second segment. A portion of the conductor member is electrically insulated from an ambient fluid by the non-conducting fluid. A first biasing member is provided for maintaining a conducting pathway between the first segment and the second segment.
In accordance with another aspect of the present invention, a downhole tool is provided that includes a housing with an external vent and a mandrel telescopically positioned in the housing. The mandrel and the housing define a chamber in fluid communication with the vent. The mandrel has a first pressure area in fluid communication with the chamber and a second pressure area of substantially equal area to the first pressure area whereby ambient fluid pressure acting on the first and second pressure areas hydrostatically balances the mandrel. A conductor member is insulatingly positioned in the housing for providing an electrically conducting pathway. The conductor member has a first segment and a second segment. The first segment is moveable with the mandrel and relative to the second segment. A first biasing member is provided for maintaining a conducting pathway between the first segment and the second segment.
In accordance with another aspect of the present invention, a downhole tool is provided that includes a housing and a mandrel telescopically positioned in the housing. The mandrel and the housing define a pressure compensated substantially sealed chamber containing a volume of a non-conducting fluid. A conductor cable is positioned in the housing for providing an electrically conducting pathway through the housing. The conductor cable is sealed from the ambient fluid pressure and has a sufficient length whereby the conductor cable is operable to elongate when the mandrel and the housing are telescopically moved away from one another.
In accordance with another aspect of the present invention, a downhole tool is provided that includes a housing with an external vent and a mandrel telescopically positioned in the housing. The mandrel and the housing define a chamber in fluid communication with the vent. The mandrel has a first pressure area in fluid communication with the chamber and a second pressure area of substantially equal area to the first pressure area whereby ambient fluid pressure acting on the first and second pressure areas hydrostatically balances the mandrel. A conductor cable is positioned in the housing for providing an electrically conducting pathway through the housing. The conductor cable is sealed from the ambient fluid pressure and has a sufficient length whereby the conductor cable is operable to elongate when the mandrel and the housing are telescopically moved away from one another.